The present invention relates generally to electronic modules and more particularly to a butt joined opto-electronic module operating at millimeter wavelength frequencies.
Recent advancements in optical communications technology have demonstrated optical data demuxing at a speed of over 160 Gbit/sec through a single mode optical fiber. At the same time, there is a lack of corresponding progress in test and measurement instrumentation to support analyzing these fast optical pulses. Current solutions are limited by interconnect issues that limit bandwidth and signal integrity, and manufacturing issues that can substantially increase the cost of components. One commercial solution is to couple an enclosed photodetector module with a conventional enclosed sampling head using a coaxial transmission line. The coupled modules are mounted in an optical plug-in module for a sampling oscilloscope. Another solution is to buy a high-speed photodetector as the optical-to-electrical (O/E) converter and use a sampling oscilloscope to capture the signal. This approach seems more beneficial for users because, in addition to having to spend less money, they can also maintain the electrical input to the scope for other testing needs. The inconvenience to users is that the screen is no longer calibrated for accurate power measurements. However, this inconvenience can be overcome by purchasing a separate power meter and perform a calibration manually. Users are faced with the choice of spending more money for the added power level calibration feature of an optical plug-in module or save $10 to 15 thousand dollars by buying a photodetector separately such that both electrical inputs and optical inputs can be measured with the same investment. The latter choice also provides users with a power meter which can be used elsewhere as well.
A common weakness for the above two solutions is that they both need electrical interconnections to connect the photodetector output to the sampler input. Because of the high frequencies involved, the connectors are quite expensive. Moreover, aside from introducing additional costs to the system, these components also introduce unwanted impedance mismatching that produce signal reflections. These signal reflections result in waveform distortion as a function of bit pattern when measuring fast repetitive signals, such as the RZ 40 Gb/Sec optical data.
A solution to these problems is to combine the detector and sampler semiconductor devices together to form a fully integrated photodetector-sampler IC design. This would eliminate all of the interconnecting hardware between the photodiode and sampler. While a fully integrated photodetector-sampler design (FIPS) sounds good, it runs into practical problems during implementation. Generally, test equipment manufactures are not vertically integrated companies that have the processing technology or the equipment to produce FIPS designs. In addition, high speed photodetector manufacturers generally specialize in producing optical components, such as O/E and E/O converters, but not electrical components, such as electrical samplers. Conversely, electrical component manufactures do not manufacture optical components. To produce the FIPS design would require capital investment and technology development by optical or electrical component manufactures or the test and measurement equipment manufacturer.
Another issue with the FIPS design is yield loss of the final assembly if either of the optical detector or sampler sections develop problems. The photodiode performance cannot be accurately characterized until permanently mounted on or within a carrier or housing, an optical fiber aligned to the photodiode, and electrically coupled to the sampler section. If the output of the competed FIPS device does not meet design specifications, it is difficult to determine if the problem has to do with the fiber alignment, photonic and impulse responses of the diode, polarization sensitivity and the like in the optical detector section or signal gain, sensitivity and the like in the sampler section. Even if the performance problem can be identified to one of the sections, replacing the defective section may lead to damage of the other section.
Another problem with the FIPS design is negotiating refunds on defective parts. Since different manufacturers make the components for the optical and sampler sections and one or the other or a system integrator, such as the test and measurement manufacturer, performs the final integration, determining the cause of the failed part or parts in the sections can be a source of conflict. For example, the problem may be determined within the photodetector module, say a lower than spec photo response. The problem could have been caused by the photodiode die being damaged during the FIPS processing; the optical fiber being misaligned from the integrator assembly process; the optical fiber end surface polishing being flawed; the fiber/detector IC junction having foreign contaminations not readily visible to the eye; the wire bond from the detector IC to the sampler IC having excessive inductance introduced by improper wirebonding; the wirebonder damaging the detector IC by improper bonding control, such as excess bond head ultrasonic energy or pressure, and the like. The photodetector IC manufacturer may be reluctant to refund the cost of the multi-thousand dollars detector IC where the defect is caused by a defective assembly process.
What is needed is an electronic module design that overcomes the shortcomings of the FIPS and the coaxial interconnect designs. The electronic module design should allow independent testing and verification of separate sections of the assembly prior to final assembly or integration. The electronic module should allow for easy assembly and alignment of the separate device sections down to the micron level.
Accordingly, the present invention is to a butt joined opto-electronic module for millimeter wavelength frequencies that allows independent alignment of coplanar transmission structures formed on opto-electrical and electrical elements in a proximate abutting relationship. The opto-electrical and electrical elements are mounted on respective independently positioned and mechanically joined open end face carrier and housing. The butt joined opto-electronic module has a housing with juxtaposed shallow and deep cavities defining an open end face between the shallow and deep cavities. An electrical element is positioned in the shallow cavity and has an electrical device formed on at least one horizontal surface of the electrical element. The deep cavity has at least a first upward extending strut with the upper portion of the strut having a securing member formed therein. A carrier is positioned on the strut and had an open end face and opposing horizontal surfaces. The carrier has at least a first tine extending from the carrier that engages the strut. An opto-electrical element is positioned on the carrier with an opto-electrical device formed on at least one horizontal surface of the opto-electrical element and coupled to receive an optical signal from an optical waveguide secured to the carrier.
Each of the opto-electrical and electrical elements has a coplanar transmission structure formed on one of the horizontal surfaces. Each coplanar transmission structure is electrically coupled to one of the respective opto-electrical and electrical devices. The coplanar transmission structures are independently aligned in three mutually perpendicular planes and positioned in a proximate abutting relationship. The carrier and/or the housing are linearly and rotationally positionable in three mutually perpendicular planes relative to the open end faces to align the first and second coplanar transmission structures. The carrier and the housing are independently positioned in a proximate abutting relationship at the open end faces and mechanically joined together as a single assembly by securing the carrier tine to the securing member of the strut by soldering, applying an adhesive or the like. Substantially flat electrical conductors, such as wedge bonded electrical conductors, electrically couple the first and second coplanar transmission structures together. The housing has a removable top cover mounted over the shallow and deep cavities.
In a first embodiment, the securing member is an axial bore formed in the upper portion of the strut. The tine extends from the under side of the carrier and is positioned in the axial bore. In the preferred embodiment, the housing has a second upward extending strut having a securing member formed in the upper portion of the strut. The securing member has upward extending tabs extending from the top of the struts defining a recessed region between the tabs. The carrier has opposing side surfaces with tines extending from each of the side surfaces. The tines are received in the recessed regions of the struts. The carrier is secured to the housing by applying a bonding material to the tines and the struts. The bonding material may include a low temperature solder, a strong adhesion low melting temperature metal, and adhesive, such as epoxy, and the like.
One or both of the opto-electrical and electrical elements may be positioned on the carrier and in the shallow cavity of the housing away from the open end faces of the carrier and the housing. One or both of the opto-electrical and electrical elements may also extend to the open end faces of the carrier and the housing or one or both may extend past the open end faces of the carrier and the housing. Each of the elements may be positioned on their respective carrier and shallow cavity in any of the above positioning relationships so long as the proximate abutting relationship of the coplanar transmission structures produces a sub-millimeter separation between the ends of the coplanar transmission structures. For example, the opto-electrical element may be set back from the open end face of its carrier and the electrical element may extend past the open end face in the housing.
A mounting dielectric substrate may be mounted on one or both of the carrier and the shallow cavity in the housing. Each substrate has an end face that may be positioned away from the open end faces of the carrier and the housing, extend to the open end faces of the carrier and the housing, or extend past the open end faces of the carrier and the housing. The opto-electrical and electrical elements are secured to the mounting dielectric substrates with each element positionable away from, extending to or extending past the end face of its mounting dielectric substrate. Multiple positioning combinations of the substrate or substrates may be combined with the multiple positioning combinations of the opto-electrical and electrical elements. For example, the opto-electrical carrier may have the mounting dielectric substrate positioned away from the open end face of the carrier with the opto-electrical element extending past the end face of the mounting dielectric substrate. The electrical element may be positioned in the shallow cavity of the housing with the electrical element extending past the open end face in the housing. In another example, the carrier and the shallow cavity may each have a mounting dielectric substrate mounted thereon. The mounting dielectric substrates may both extend past the open end faces of the carrier and the housing with the opto-electrical and electrical elements extending past the end faces of their respective mounting dielectric substrates.
The opto-electrical module may also have a standoff dielectric substrate positioned in an abutting relationship with at least one of the opto-electrical and electrical elements. The standoff dielectric substrate has opposing vertical walls and a horizontal surface on which is formed a coplanar transmission structure. The coplanar transmission structure on the standoff dielectric substrate extends to two of the opposing end walls of the substrate and is positioned in a coplanar relationship with the abutting opto-electric or electrical element and electrically couple via substantially flat electrical conductors. The coplanar transmission structures of the standoff dielectric substrate and the other of the opto-electrical and electrical elements are independently aligned in three mutually perpendicular planes and positioned in a proximate abutting relationship. The invention may also be implemented with a standoff dielectric substrate abutting each of the opto-electrical and electrical elements with the coplanar transmission structures of the standoff dielectric substrates being independently aligned in three mutually perpendicular planes and in a proximate abutting relationship. One end wall of each of the standoff dielectric substrates may be positioned away from the open end faces of the carrier and the housing, extend to the open end faces of the carrier and the housing, or extend past the open end faces of the carrier and the housing. The standoff dielectric substrate or substrates may mounted on a mounting dielectric substrate or substrates with the standoff dielectric substrates. One end wall of each of the standoff dielectric substrates may be positioned away from the end face or faces of the mounting dielectric substrate or substrates, extend to the end face or faces of the mounting dielectric substrate or substrates, or extend past the end face or faces of the mounting dielectric substrate or substrates.
The opto-electrical device formed on the opto-electrical element may be an optical-to-electrical converter, such as a photodiode, a semiconductor laser, an optical modulator or other types of devices that receives an electrical signal to generate or modulate an optical device or generates an electrical signal in response to a received optical signal. The electrical device formed on the electrical element may be at least a first sampling diode of a sampling circuit, a laser driver, an amplifier or the like.
The objects, advantages and novel features of the present invention are apparent from the following detailed description when read in conjunction with appended claims and attached drawings.